1. Field of the Invention
The present invention relates to a process for producing titanium trichloride compositions suitable for use as the transition metal component of Ziegler-type catalysts. More specifically, the present invention relates to a process for producing a Ziegler-type catalyst component for the polymerization of .alpha.-olefins having high stereospecificity and polymerization activiy by reducing and activating titanium tetrachloride according to a particular embodiment of the invention.
The present invention provides a process for producing highly stereospecific .alpha.-olefon polymers with a high yield.
2. Description of the Art
It is well known that Ziegler-type catalysts are used as catalysts for the stereospecific polymerization of .alpha.-olefins. It is also well known that titanium trichloride is first named as a transition metal compound which is one of the primary components of the Ziegler-type catalysts. The titanium trichloride is combined with an organoaluminum compound which is the other primary component to form a Ziegler-type catalyst.
The titanium trichloride is prepared by reducing the titanium tetrachloride. Ordinarily, titanium trichloride which contains the reduction reaction products of a reducing agent and other materials is used as a titanium trichloride composition for the catalyst component.
As one of the titanium trichloride catalyst components which have been widely used for industrial purposes, a titanium trichloride catalyst component is known which is prepared by reducing titanium tetrachloride with an organoaluminum compound or metallic aluminum. The titanium trichloride catalyst component so prepared is a titanium trichloride composition containing a certain amount of aluminum chloride (for example, about 1/3 mole of aluminum chloride per one mole of titanium trichloride).
In polymerizing olefins by using a Ziegler-type catalyst containing such a titanium trichloride composition, it is naturally required that the stereospecificity of the resulting olefin polymers be as high as possible and that such polymers be produced with as high a yield as possible. Various studies have been made to develop a catalyst capable of satisfying such requirements. Most of the studies appear to be directed to an improvement in the titanium trichloride composition.
For example British Pat. No. 1,391,068 discloses a process for producing a titanium trichloride composition which comprises reducing titanium tetrachloride with an organoaluminum compound, treating the resulting reduced solid (viz. titanium trichloride composition) with a complexing agent and further contracting the solid so treated with titanium tetrachloride. A Ziegler-type catalyst composed of the titanium trichloride composition so obtained has high activity and, at the same time, imparts good stereospecificity to the resulting olefin polymer. Accordingly, it can probably be stated that the titanium trichloride composition of the above mentioned British Patent is one of the best compositions which have been hitherto proposed.
The titanium trichloride prepared by reducing titanium tetrachloride with the oganoaluminum compound according to the known method is a .beta.-modification or .beta.-form in its crystal form. It is believed that the .beta.-titanium trichloride is converted into a .gamma. - or .delta.-titanium trichloride by further treating the .beta.-modification with the complexing agent and titanium tetrachloride. In this case, it seems to be essential for obtaining high activity that the titanium trichloride produced by the reduction be of .beta.-modification and this .beta.-titanium trichloride be converted into other crystal structures.
That is, a process for treating a titanium trichloride composition obtained by reducing titanium tetrachloride with metallic aluminum instead of the organoaluminum compound in the same procedure described above has been proposed (as in British Pat. No. 1,370,559). In this process, the titanium trichloride produced by the reduction is a .beta.-modification in its crystal form, and a Ziegler catalyst composed of a titanium trichloride composition resulting from the starting .gamma.-titanium trichloride is far less active than a Ziegler catalyst composed of the titanium trichloride composition resulting from the titanium trichloride (.beta.-modification) prepared by the reduction with organoaluminum compound.
On the other hand, U.S. Pat. No. 3,032,510 discloses a process for improving the polymerization activity of a Ziegler catalyst by dry-pulverzing a titanium trichloride composition which can be ordinarily used as a catalyst component for the stereospecific polymriization of .alpha.-olefins. However, as is fully described hereinafter, the pulverizing treatment does not always provide an improvement in activity.